This invention relates generally to the testing of electronic integrated circuits, and more particularly the invention relates to sockets for receiving packaged integrated circuits for test purposes.
The packaged integrated circuit typically includes a polymer or ceramic housing for a semiconductor chip with electrical leads extending from the package which are electrically connected to the semiconductor chip. In a dual in-line package (DIP), the electrical leads are arranged in two parallel rows with the leads depending from the bottom of the housing.
Packaged integrated circuits must undergo a number of different tests, each test requiring the insertion of the integrated circuit package and leads into a test socket. To prevent bending or damage to the leads, zero insertion force (ZIF) sockets have been devised to limit the force exerted on the leads when the package is inserted into a test socket. The most widely known and used ZIF sockets are from 3M Corporation and Aries Corporation. In these sockets the leads of a DIP (dual in-line package) are pinched between two pieces of metal which are, in turn, soldered to a printed circuit board. The metal pieces are held in place by the body of the ZIF socket which is typically made of plastic. The metal pieces are electrically conducting to provide a good electrical path from the DIP lead to the printed circuit board in which the ZIF socket is attached. In all cases, the bodies of these sockets are made of some organic material (plastics or polymers) which can only withstand temperatures as high as 250 degree C. for extended periods of time. The metal used to pinch the leads of the IC DIP packages are beryllium copper alloy or beryllium nickel alloy for a high temperature operation not to exceed 250 degree C. While these sockets perform well within their stated specifications, they cannot be used at temperatures in excess of 250 degree C. because the materials will decompose and fail.
U.S. Pat. No. 6,179,640, assigned to the present assignee, discloses a test socket including two members having planar surfaces arranged to permit relative lateral movement between the two members. One member is a package support and has a plurality of holes extending therethrough for receiving the integrated circuit package leads. Each hole has sufficient size to receive a lead with minimal or no force. The second member is a contact support and has a plurality of contact wires arranged to be in spaced juxtaposition with package leads when a package is inserted into or removed from the support member. The contacts are slidable into engagement with the package leads after the package is inserted.
FIG. 1A is a plan view of contact support 10 of ZIF socket 8 in accordance with xe2x80x2640 Patent with spring wires 12, 14 providing contacts for leads of an integrated circuit package (not shown) which extend through holes 16, 18 in package support 11 of socket 8. Wires 12, 14 are arranged in parallel groups of wire which are anchored to the socket in holes at opposing ends 20, 21 and 22, 23. Vertical separation of the rows of holes 16 and 18 may be 0.3 inch to accommodate an industry standard I.C. package called xe2x80x9cnarrow DIPxe2x80x9d. FIG. 1B shows package support 11 slid relative to contact support 10 whereby wires 12, 14 are moved from holes 16, 18 and permit the insertion of leads of an integrated circuit package into holes 16, 18.
FIGS. 2A, 2B represent the same ZIF socket of FIG. 1, but now engaged by leads or pins 30, 31 of UUT 32. For clarity, the main body of UUT 32 has been removed from FIG. 2B to expose the underlying interaction between pins 30, 31 and spring wires 12, 14.
It will be noted that the socket holes 16, 18 are not located midway between the anchor points of the wires, but rather the length of the wire sections that lie underneath the body of the UUT are significantly shorter than the wire sections that lie outside of the UUT 32. This causes the shorter inner wire sections to distort more than the longer outer sections.
In order for the spring wire contacts to perform well, a certain amount of reasonable xe2x80x9cworking distancexe2x80x9d must be provided between the anchor points and the contact points. If the working distance is too small, damage to either the UUT pins or the spring wires can result. Experience shows that the smaller the working distance, the more difficult the overall design of the ZIF mechanism, especially in terms of allowing tolerances of the socket components. Consequently, a low working distance can have significant adverse ramifications in terms of both cost and reliability of the final product.
The present invention is directed to increasing the working distance in such a ZIF socket.
In accordance with the invention, wire contacts in a contact support plate of a ZIF test socket are arranged in two parallel partially interdigitated sets to thereby increase the minimum working distance between contact points on the wire and anchor points at either end of the wire. The wires are inclined with respect to the alignment of lead receiving holes in the package support plate to allow for the interdigitation of the sets of wires. Thus the working distance of the wire under the DIP package is not limited to less than half the width of the package.
The invention and objects and features thereof will be more readily apparent from the following detailed description and dependent claims when taken with the drawing.